[Haskell-cafe] Re: A type class puzzle

Greg Buchholz wrote:

I guess it just looks really strange to my eyes. For example, "foo" and "bar" are legal, but "baz" isn't. That's what I was thinking of the situation, but I guess the type classes iron out the differences.

Ah, but here 'baz' is illegal because of the (somewhat arbitrary) restriction that different lines of a function binding must have the same number of "argument patterns". The different instances of 'BuildList' have unrelated definitions of 'build\'' - at least as far as this restriction is concerned.